This invention relates to a circuit for interfacing an electronic engine control unit (ECU) to an exhaust gas oxygen sensor, and more particularly to a circuit that can be configured by the ECU to work with different types of oxygen sensors and to diagnose the operation thereof
In a motor vehicle engine control system, engine fueling is controlled by a closed-loop control system that includes one or more exhaust gas oxygen sensors, and a corresponding number of circuits for interfacing the oxygen sensors with an electronic controller. Electrically, the oxygen sensor can be characterized as a two terminal analog device, and the interface circuit functions not only to develop a suitable input for the controller, but also to diagnose electrical faults such as shorts and open-circuits. See, for example, the U.S. Pat. No. 5,467,034 to Manlove et al., issued on Nov. 14, 1995, assigned to the assignee of the present invention, and incorporated herein by reference. As described in Manlove et al., the interface circuit can include RC filter elements to remove unwanted noise and a bias voltage to diagnose cold sensor and open-circuit fault conditions. However, oxygen sensors produced by different manufacturers require unique interface circuitry, and leakage paths between the sensor terminals and ground and/or battery make it difficult or impossible to reliably distinguish a normally operating rich-condition sensor from an open-circuit. Accordingly, what is needed is an improved interface circuit that is flexible enough to work with sensors produced by different manufacturers and to reliably diagnose sensor failures.
The present invention is directed to an improved oxygen sensor interface circuit that is configurable on the fly by an electronic controller such as an engine controller to support oxygen sensors having unique interface requirements, to reliably identify various oxygen sensor faults, and to enable rapid detection of a warmed up sensor. According to the invention, the interface circuit is configurable in a first respect to enable operation with any of a number of different sensors, and in a second respect to enable more reliable fault detection, including measurement of leakage to ground or battery.